1) Field of the Invention
The present invention relates to a conductive resin composition, and more particularly to a conductive resin composition significantly improved tensile elongation, impact strength and further moisture absorbability without deterioration of heat resistance by adding a conductive material and oxazoline ring-containing compound to an aromatic polycarbonate resin and optionally a specific polyester resin.
2) Background Art
Previously, conductive resin compositions have been widely utilized as parts and packaging materials in the electric and electronic fields. Examples of the conductive resin compositions generally used include conductive resin compositions to which conductive materials such as carbon black, carbon fiber, graphite, metal fillers and metal fiber are added. In particular, conductive resin compositions containing carbon black have been widely used mainly in industry because of their excellent economy.
The use of carbon black can relatively easily give conductivity to resins, but include the following problems. That is to say, carbon black is in the form of an extremely fine powder, so that it has a high surface activity, resulting in essential poor compatibility with many kinds of resins. For that reason, the compounding of carbon black requires a large amount of mechanical energy, and therefore, the resins are exposed to severe thermal circumstances in many cases. Further, in order to obtain conductivity, the addition of a relatively large amount of carbon black is required, so that the essential mechanical properties of the resins are liable to deteriorate. Consequently, the finally compounded resin compositions have the problem that they are generally brittle and poor in mechanical strength.
In such a situation, as a method for improving mechanical strength, giving attention to carbon black, the use of carbon black developed in structure having a DBP oil absorption of 300 ml/100 g or more is proposed. According to this method, the conductivity can be obtained by the addition of a relatively small amount of carbon black, so that the relative weight of carbon black to resins can be reduced. However, the volume percentage of carbon black added is high because of its very high bulk specific gravity, even if the weight thereof is decreased. Accordingly, the mechanical strength of the resulting compositions is not necessarily satisfied.
Conductive polycarbonate resins containing carbon black have recently been used as general purpose engineering plastics, for example, as parts and packaging materials in the electric and electronic fields, and it is expected that the demand therefor will be substantially increased after this, because they are excellent not only in the balance of heat resistance and strength, but also in economy. However, many of the commercial conductive polycarbonate resins are difficult to say that the heat resistance and strength characteristics are sufficiently exhibited, as described above.
On the other hand, as a method for inhibiting a decrease in mechanical strength, the addition of a thermoplastic elastomer or a rubber component as a third component is proposed. This method is a general method widely used for improving the impact strength of a resin filled with an ordinary filler. In the present circumstances, however, the impact characteristics are not improved so much for a decrease in thermal deformation temperature, although the impact strength is improved in many cases. In particular, under circumstances where the amount of the third component added to a resin requiring the heat resistance can not but be limited, things are not in a satisfactory situation.
Resins having moisture absorbability are generally polar resins having hydrophilic functional groups in many cases. Methods for inhibiting the moisture absorbability include, for example, a method for inhibiting the moisture absorbability by polymer alloy with a resin low in moisture absorbability. However, although the relative moisture absorbability can be decreased, fluctuations in local moisture-absorbed sites are produced according to the dispersed state.
Further, there is a method of introducing a functional group such as a benzene ring which can stereostructurally prevent the attack of water molecules into a site adjacent to a polar group by polymerization. According to this method, however, the original properties of a resin may be substantially changed, so that it is difficult to apply this method to usual resin blending techniques.
Furthermore, from the viewpoint of the compatibility with a resin, a method of dispersing a relatively low-molecular substance at the molecular level is also conceivable. However, the heat-resistant characteristics and strength characteristics of the resin is deteriorated by the influence of the low-molecular substance.
The polycarbonate resins are resins relatively low in moisture absorbability. However, they considerably absorb moisture under the circumstances of high temperature and humidity, because they have ester structures as main chains.
As described above, in the present circumstances, it is difficult to improve the strength characteristics and further the moisture absorbability of the carbon black-containing polycarbonate resins without deterioration of the original characteristics thereof.